Battery plates comprising a multiplicity of perforated metallic foil elements and a battery utilizing same

ABSTRACT

Battery plates for acid or alkaline batteries are made up of a multiplicity of perforated metallic foil elements stacked in face-to-face contact. The foil elements carry a surface deposit of battery active mass and the numerous perforations through the foil surfaces are generally uniformly distributed over the surface area. The holes in each foil element are substantially in register with the holes in the next adjacent foil element. In the stack, the foils are separated from one another by layers of battery active mass of at least twice the thickness of the foils. Electrical contact, in parallel among the foils, is attained by welding (or by other means of attaining a metallic conductive path) only at the periphery of the stack.

United States Patent 1 91 Edwards et a1.

BATTERY PLATES COMPRISING A MULTIPLICITY 0F PERFORATED METALLIC FOIL ELEMENTS AND A BATTERY UTILIZING SAME, Inventors: Joseph Edwards, Bishopston, Wales;

John Edward Whittle, Sutton Coldfield, both of England The International Nickel Company, Inc., New York, NY.

Filed: Jan. 31, 1972 Appl. No.: 222,019

Related U.S. Application Data Continuation-impart of Ser. No. 28,929, April 15, 1970, abandoned. 1

Assignee:

US. Cl 136/6 R, 136/24, 136/28,

- 136/70 Int. Cl. HOIm 43/04 Field of Search 136/36, 37, 50, 64, 136/65, 75-78, 19,.20, 24, 28, 29, 30, 26-27, 6,120,143, 70, 68; 204/1 l13, 56

References Cited UNITED STATES PATENTS 1/1909 Cole 136/143 2/1914 Hub'bellm. 136/24 l/l922 Edison 136/28 1 Jan. 15, 1974 2,928,888 3/1960 Vogt 136/6 3,069,486 12/1962 Solomon ct al.... 136/30 3,320,139 5/1967 Golbcn et al. 204/35 3,305,401 2/1967 Aulin 136/120 3,441,440 4/1969 Silverstone 136/29 OTHER PUBLICATIONS J. McCallum et al., Development of Largelnternal-- Surface-Area-Nickel-Metal Plaques, Sept., 1965-Batelli Memorial Institute.

Primary ExaminerAnthony Skapars Attorney-Maurice L. Pine! [57] ABSTRACT Battery plates for acid or alkaline batteries are made up of a multiplicity of perforated metallic foil elements stacked in face-to-face contact. The foil elements carry a surface deposit of battery active mass and the numerous perforations through the foil surfaces are generally uniformly distributed over the surface area. The holes in each foil element aresubstantially in register with the holes in the next adjacent foil element. In the stack, the foils are separated from one another by layers of battery active mass of at least twice the thickness of the foils. Electrical contact, in parallel among the foils, is attained by welding (or by other means of attaining a metallic conductive path) only at the periphery of the stack.

7 Claims, 2 Drawing Figures BATTERY PLATES COMPRISING A MULTIPLICITY OF PERFORATED METALLIC FOIL ELEMENTS AND A BATTERY UTILIZING SAME This is a continuation-in-part of application Ser. No.

28,929, filed Apr. 15, 1970, now abandoned.

The present invention relates to the construction of plates for use in acid or alkaline batteries.

The plates for alkaline batteries may be constructed in a number of well-known ways, for example, as tubular plates, pocket plates or sintered plates. The actual Turner, filed July 16, i969, now U.S.- Pat. No.

3,579,383. In the case of the negative plate the battery active mass is cadmium and this is conveniently depositedon the nickel foil by electrodeposition in the manner described by I.H.S. Henderson and 3.0. Ladan in an article entitled The Preparation and Structure of Electrodeposited Sponge Cadmium Electrodes, Canadian Journal of Chemical Engineering, Vol. 46, Oct., 1968, pages 355-363. A nickel-cadmium battery of the i type described will also include an alkaline electrolyte such as, for example, a solution of potassium hydroxide.

In the case of nickel-iron or nickel-zinc batteries, the negative plate may again be made of nickel foilbearing a deposit of iron or'zinc or hydroxides of these metals, this battery active mass being produced by electrodeposition from solutions containing suitable salts of iron or zincsuch as, for example, ferrous sulfate, ferrous chloride or zinc cyanide.

In providing plates for acid batteries in accordance with the invention, the foil iscomposed' of a lead alloy or dispersion strengthened lead and the battery active mass at the positive plate is pr'ovidedin'the form of lead dioxide while at the negativepla'te the battery active mass is sponge lead. Such a battery would contain a solution of sulfuric acid as electrolyte.

In all designs of plate, whether for acid of alkaline batteries, clearly the battery 'active mass must be supported in such a way that theelectric current flowing through the electrolyte can have easy access to it while at the same time, the battery active mass must be in intimate electron transfer relationship with the support which provides a metallic path for carrying electric current between the battery and that part of a circuit external of the battery. A plate construction inwhich such ready access and electron transfer-relationship can be optimized, depending on the use for which the battery is intended, has now been discovered.

It is an object of the present invention to provide an improved battery plate constructed from perforated metal foil.

It is another object of the invention to provide a battery plate comprised of multiple layers of perforated nickel foil. V

Other objects and advantages will become apparent from the drawing taken in view of the following description, in which FIG. 1 depicts a-battery plate of the present invention and FIG. 2 is a highly enlarged crosssectional view of the battery plate of FIG. 1 along the line 22.

Generally speaking, the present invention is directed to the construction of a battery plate formed from'perforate metal foil elements having battery active mass on the surfaces thereof, the foil elements being stacked in face-to-face contact with substantially all the perforations in the foil elements in register and being electrically connected in parallel only at the periphery of the stack. v

While the structure set forth in this invention is suitable for plates for both acid and alkaline batteries, the description which follows illustrates the invention in terms of plates for use in alkaline batteries. Further, while the invention is not limitedin any way to nickel foil for use in battery plates, and the foil may be made of any metal suitably resistant to chemical or electrochemical attack in the battery electrolyte, nickel foil is used as the vehicle of description since both positive and negative plates of most forms of alkaline batteries are conveniently made using nickel as the support.

A battery plate in accordance with theinvention is depicted in the drawing. Referring now thereto, battery plate 11 is made up of a plurality (i.e., at least three) of perforated metallic foil elements 12 which, as depicted are rectangular, but canbe of any convenient shape. Active battery mass 13 which covers substantially all of the surface of foil elements 12 separates metallic foil elements 12 and forms the outersurfaces of battery plate 11 except for edges 14 which are welded. Welded edges 14 effectively interconnect metallic foil elements 12 in parallel. Tab 15, also welded to at least one foil element 12 providesmeans for connectingbattery plate 11 in a conventional battery assembly.

Holes 16 and 17 serve to register perforations 18 in each of foil element 12 each with each other to provide passages which pass through battery plate 11. Perforations 18 are geometrically arranged in each of foil elements 12 so as to be substantially uniformly dispersed across the surface of foil element 12 and occupy about 3 percent to about 50 percent of the area of foil element 12. Battery active mass 13,-which is microporous in nature, is situated so as not to block perforations 18. In use, the passages provided byre'gistration of perforations l8 -permit relatively free flow of low resistance electrolyte into the interiorof battery plate 11 and direct contact with batteryactive mass adjacentsaid passages. Electrolyte trapped in the micropores of the bat-- tery active mass is thus in directcontact withfree (or mobile) electrolyte providing relatively short paths of high electrical resistance within the battery plate. By closely spacing perforations 1 8 in foil elements l2 and limiting the total area of perforations 18 to about 5 percent to about 15 percent ofthe area of battery plate 1 I, one achieves a battery electrode having both a high energy density and high efficiency at high discharge rates. For any given ratio of thickness of active battery mass to metallic foil increasing the perforation area results in lowering energy density and, within limits, increasing the number of perforations per unit area increases the efficiency at rapid discharge rates and vice versa. Increasing the ratio of thickness of active battery mass to the thickness of the metalfoil increases the energy density of the plate while at the same time increases the internal resistance of the plate. As a minimum, given metallic foils of a thickness of about 0.002 centimeter, the battery active mass separating each pair of foils should be about 0.004 centimeter thick, i.e., a ratio of about 2 to 1. More advantageously, the

.ratio is about 6 to l to about 40 to 1. When the ratio is as high as 60 to 1 a battery plate is obtained which has extremely high energy density but is limited by having a low discharge rate.

Preferably the perforated foils have been produced by electroforming, a process which is well known, and which is described, for example, in a paperentitled Electrowinning of Nickel Screens by J. van der Waals, which is abstracted in Electroplating and Metal Finishing, Vol. 16, No. 11, Nov. 1963, pages 393-394. The electroforming process is capable of producing a nickel foil having numerous small perforations but satisfactory perforations may also be produced by mechanical means such as contacting the foil with a roll provided with teeth to punch the desired holes. Advantageously, the foils will also have two or more relatively larger holes through them whereby they can be aligned by means of a spigot, so that the perforations in the assembled plate are in register. Registration of the perforations in the battery plate is important because, in the absence of such registration, access of current to the interior of the plate is restricted and there is a sharp rise in the internal resistance of the plate.

The metal foils will normally be extremely thin, and in the case of nickel it is generally desirable to use foil having a thickness of from 0.0004 cm to 0.005 cm, most advantageously at the lower end of this range. The active mass produced on foil of this thickness (which in the case of nickel foil used as positive electrodes for nickel-cadmium batteries is nickel hydroxide) will itself normally have a thickness of between 0.0005 cm and 0.009 cm. To provide ratios of thickness of battery active mass to thickness of an adjacent foil of about 2 to l to about 36 to l when registered foils are stacked. The active mass may be present on one side'or on both sides of the foil and will be deposited on the walls of the perforations. It is beneficial to have battery active mass on both sides of the foils and then to stack sufficient foils in contact face-to-face to produce a finished plate of about 1 mm. thickness. Clearly the thickness of the stack can be smaller or greater than this, depending on the purpose for which the battery is made. High discharge rates demand relatively thin plates; thicker plates are more economical in the number of separators required but beyond a certain point the gain in en- I ergy density resulting from the use of fewer separators is fully offset by the loss resulting from-the need to increase the area of the perforations in the foil in order to avoid undue increase in the resistance to penetration by the current into the interior of the plate.

It has been found that the shape of the perforations and the position of the perforations in the foil are important to the functioning of a plate according to the invention when operating within a battery. The internal resistance of the plate and the output of the plate may be controlled by suitable choice of the size, distribution and shape of the holes. Thus the total area of holes per unit area of foil is determined by the plate-thickness 'chosen and the service requirements of the battery in a small proportion of the area of the foil', generally speaking this proportion will be at least 3 percent, but

will not exceed 50 percent, and good results are obtained when the proportion is from 5 percent to 15 percent. It is desirable that the holes should be uniformly distributed and individually small, say from 0.01 mm to 1 mm in area. By choosing the smallest size of the hole consistent with practical considerations of manufacture and stacking the number of holes per unit area can be made as large as the limit on total hole area will allow, and in this way, the distance between adjacent holes is made as small as possible. With a given total hole area, decreasing the size of individual perforations decreases the spacing between the holes and thereby lowers the internal resistance of the plate. Generally, there will be between 4 and 4,000 holes per square centimeter in the foils employed for the purposes of this invention. Compared with a circular shape there is the advantage to be gained from elongated holes that the total hole periphery is increasedfor a given total hole area and this lowers the internal resistance of the plate by improving access of the current to the active mass.

In all batteries, the plates of opposite polarity need to be spaced apart with separators to prevent contact between them. At the same time it is necessary for the ions in the electrolyte to be able to pass through the separators. Suitable separators may be made from a wide variety of insulating materials including nylon, polypropylene and polytetrafluoroethylene. Depending on the type of separators used, it may be advantageous to arrange for the separators to possess perforations similar to those provided in the plates and furthermore to arrange the construction of the battery so that the perforations in the plates and in the separators are in register to facilitate rapid movement of the ions in the electrolyte As an example, two plates were prepared in similar fashion, each 2.54 cm square and 0.0178 cm thick with 10 layers of electroformed nickel foil of 0.0005 cm thickness. The nickel foil elements bore a layer of battery active mass 0.0007 cm thick composed of nickel hydroxide. This battery active mass was formed by placing the perforated nickel foil elements in a solution comprising 250 parts by volume of a solution of Ni(- NO '6H O having aconcentration of 750 grams per liter, 6.25 parts by volume of concentrated l-lNO solution and 20 parts by volume of NH; solution (specific gravity 0.880). A current of 5 milliamperes per square centimeter was passed for a period of 15 minutes to develop the desired layer of battery active mass on both sides of the foil.

ln plate 1, the nickel foil had 11 perforations per square centimeter, and in plate 2, the nickel foil had 174 perforations per square centimeter, the radius of the holes and the center-to-center distance between adjacent holes in plate 1 being 0.0526 cm and 0.322 cm and in plate 2 being 0.0121 cm and 0.079 cm. The total area of the holes in the case of plate 1 was about 10 percent and in the case of plate 2 was about 8 percent. In the plates, the foil perforations were substantially in register'and the foils were welded together along one edge. The maximum internal resistance at completion of discharge of plate 1 was found to be 0.984 ohms, and that of plate 2 was found to be 0.105 ohms.

The plates were charged and discharged several times in potassium hydroxide solution having a specific gravity of l .29, and their capacities at different rates of discharge determined. The values obtained are given in the following Table in which mA is milliamperes and mAh is milliampere hours.

6 conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art-will readily un- 5 derstand. Such modifications and variations are consid- TABLE I ered to be within the purview and scope of the invention and appended claims. Plate Discharge Rate Time of Discharge Capacity We claim. mA (secs) mAh l. A laminate battery plate adapted to be electro- 1 130 332 13.8 chemically charged and discharged repeatedly com- 2 2 g: prising at least three foils of metal inert to battery elec- H70 308 trolyte each about 0.0004 to about 0.005 centimeter thick in parallel metal-to-metal electrical connection v positioned coextensive with and essentially parallel to The superiority of plate 2 at the higher rate of diseach other a spac.ed apart-from each by layers of substantially uniform thickness of microporous, charge is clearly shown and it exhibits the effect of the l electrochemically active battery mass adapted to be ower mternal resistance of plate 2 owing to the close f th h l saturated with electrolyte, the two outer foils each havspacmi o e 0 ing a layer of said microporous electrochemically acf h example two planes were pa fljom tive mass on the outer surface thereof, said electrode nickel foll m the form a square of 50 h being constructed and arranged so that the thickness of hess 00064 w havlhg holeicohfighrahoh the safhe said microporous electrochemically active mass sepaas for Plate 1 above and heanhg of achve rating each pair of said metallic foils is at least twice the mass on each face- The first of these Plates, Plate thickness of each said metallic foil, so that a multipliccomprised 0 u fOilS and t Second P Plate ity of uniformly dispersed, essentially parallel holes was, a single foil. These plates were charged and dis- 2 adapted to contain mobile electrolyte penetrate charged in potassium hydroxide solution as in the prethrough said electrode in a direction normal to the vious example and their capacities at different rates of pl n of Said foils at each h e 100i, Said holes being of charge determined with the results as tabulated below. a density of at least 4P5! squarecentimeter of external TABLE II Number Discharge Rate Time to Capacity Plate of foils mA mA/cm discharge Ah mAh/cm g in hours H It i l be Seen a the ap i y of the y r P H electrode area and being of diameters such that the plate 3, is close to the ideal obtained for the single layer 40 total area of said holes is about 3 percent to about 50 foil, and this remarkably small loss of capacity is truly percent of the total external area of said electrode and surprising when one considers the stacking of the 10- so that said foils are in direct metal-to-metal contact foils in a face-to-face relationship, thereby exhibiting With each other y at the. periphery thereof. the advantages of the invention. It is also important to The battery Plate ohchhm l Wherelh the fol! keep in mind when comparing plates 3 and 4 that plate mems are Composed of h 4 is not a practical plate. The single foil construction of The Plate of clam 1 where'h h hole area plate 4 lacks the rigidity required in a commercial b t does not exceed 15 percent of the total external area tery. Further, a battery made of a plurality of plates as 2 i bl l l d plate 4 would require a largenumber of separators thus attery, contammg a e e f yte an I having a plurality of battery plates therein of the type owermg the energy density of the battery tremendousl when a late is made" ofa Imam of foils set forth in claim 1 and having perforated insulating b p f 3 y d separators between adjacent battery plates with the i ex i i num er 0 emg y perforations thereof substantially all in register with the with relatively th ck foil, e.g., about 0.005 centimeter element perforations h h q. t iihih h f mechamcal 5. The battery of. claim 4 wherein the foil elements ngldlty q commerclal'use and F as Show" 55 are composed of nickel and the electrolyte is potassium by the comparison of plates 3 and 4, retain the electrohydroxide chemical advantages of a single foil plate. If metallic A battery comprising a plurality f battery plates sheets of thickness greater than about'0.005 centimeter f the type set f th in claim 2 and having f t d thick used, either the e gy dehslty the Plate insulating separators between battery plates of opposite Ploducecl with Smith Sheets so small or the lhtemal f polarity with the perforations therein substantially all in Sistance 5 h g ha h P is mp t y p lj register with the foil element perforations. cal in terms of present day battery technology. 7. The battery of claim 6 wherein the hole area of the There has thus been disclosed a relatively simple b tt late and separators does-not exceed 15 perplate structure for batteries with substantially improved cent f he external area of said battery plate or separa electrical properties, i.e., a relatively large electrical tqr,

output at high discharge rates.

Although the present invention has been described in, 

2. The battery plate of claim 1 wherein the foil elements are composed of nickel.
 3. The battery plate of claim 1 wherein the hole area does not exceed 15 percent of the total external area of said battery plates.
 4. A battery containing a suitable electrolyte and having a plurality of battery plates therein of the type set forth in claim 1 and having perforated insulating separators between adjacent battery plates with the perforations thereof substantially all in register with the foil element perforations.
 5. The battery of claim 4 wherein the foil elements are composed of nickel and the electrolyte is potassium hydroxide.
 6. A battery comprising a plurality of battery plates of the type set forth in claim 2 and having perforated insulating separators between battery plates of opposite polarity with the perforations therein substantially all in register with the foil element perforations.
 7. The battery of claim 6 wherein the hole area of the battery plates and separators does not exceed 15 percent of the external area of said battery plate or separator. 